This is another example, that for some reason these smaller cuts of meat are taking longer than bigger ones. It is an odd phenomenon that I don't really have an explanation for. We have seen it in butts and smaller brisket flats as well.
One recommendation for the next time is to start your butt around midnight for a next day evening meal. This allows you plenty of time to put it into warm mode if need be. If you are going to warm it in the smoker, I would set a step in your Auber to lower it down to 140 when the internal temp hits 190. The meat will keep cooking after it goes into warm mode and will most likely hit a top temp of very close to the desired 195 that we shoot for.
You can hold it in warm mode for several hours. Then, pull it out 1-2 hours before your meal-time, double-foil, and then rest in the cooler for 1-2 hours. Here lately I have been preferring to hold for 2 hours. After two hours, the butt is still very hot. Almost too hot to touch with bare hands, but is a perfect temp for pulling.
I would also shoot for a minimum of 7.5-10.0 pound butts in the future. We have just found that they cook more evenly and don't have quite as many surprises.